The sight of bright red blood usually scares us a little. Bright red blood always conjures up images of life, injury and death. In fact, not all animals’ blood is red, for example, shrimp’s blood is green, earthworm’s blood is rosy, some snails’ blood is transparent, praying mantis’ blood is green, and there is a strange animal called “horseshoe crab” in the sea whose blood is actually blue, but of course, there should be no blue-blooded people among the earth. The reason our human blood is red is because it contains a large amount of hemoglobin, the main component of which is iron, and the blood is bright red when it contains more oxygen (arterial blood) and dark red when it contains less oxygen (venous blood), and the main component of plasma is water, which looks transparent and yellowish because it contains a small amount of bilirubin. In principle, blood transfusion can only be performed between the same blood type and after a pairing test, otherwise it may cause serious clotting reactions and be fatal. How much blood is in each of us, and how much bleeding poses a danger to the human body? The total amount of blood in a normal person is equivalent to about 7-8% of body weight. A person who weighs about 65 kg has about 5 kg of blood all over his body. A healthy person who loses less than 500 ml of blood at one time usually does not have much problem; an acute bleeding of more than 1000 ml will cause obvious discomfort to the body, and more than 1500-2000 ml will be life-threatening if not treated in time. Blood is composed of plasma and blood cells, which in turn include three types of cells: red blood cells and white blood cells and platelets. The average lifespan of a red blood cell is 120 days, a white blood cell is 9-13 days, and a platelet is 8-9 days. However, the body constantly produces new blood cells to replenish them. The main function of red blood cells is to transport in oxygen and carbon dioxide, the main function of white blood cells is to kill bacteria, resist inflammation and participate in the process of immunogenesis in the body, and platelets mainly play a hemostatic function in the body, and a problem in any one of them can cause blood system diseases. In addition to traumatic bleeding, we need to go to the hospital emergency room for emergency treatment, there are also some blood system diseases that we usually need to go to the hematology department of the hospital, the most common blood system disease is anemia, but anemia alone is divided into adolescent anemia, iron deficiency anemia, hemolytic anemia, thalassemia, megaloblastic anemia, aplastic anemia and so on and so forth, after a series of tests to confirm the diagnosis to take It is only after a series of examinations and diagnosis that different targeted treatments can be useful. Among all kinds of human cancers, leukemia is one of the few that occurs in children and adolescents rather than in the elderly. With the continuous progress of medical technology, many types of leukemia are no longer incurable and can be completely controlled by doctors with timely treatment. In lively public places, we often see the figures of blood collection vehicles, they are mobile life. Since we were in college, we have been organizing voluntary blood donation, many people will say, where does all the blood we donate go, does blood donation hurt the body or not? Why is blood donation free of charge, while blood transfusion requires payment? The blood we donate is centralized to the central blood station, where the blood is tested again by the staff of the blood station. The unqualified blood is eliminated, and the healthy blood is then separated and prepared into component blood such as red blood cells, plasma, platelets, etc., and some of it is used as fresh blood specifically to treat critically ill patients. So modern hospitals are unlikely to have the kind of TV that rolls up its sleeves and donates blood directly to patients to be rescued – not even on the battlefield. Blood testing, separation, storage, etc. all require significant costs, so a fee is charged for the transfusion, but if you have donated blood in the past or a family member has donated blood, you can use a certain amount of blood products for free. A moderate amount of blood donation will not harm your health. A single donation of 200 to 400 ml of blood, accounting for less than 10% of the total amount of blood, will have no effect on your health, but will have many benefits. After birth, the bone marrow becomes the main blood-producing organ. The hematopoietic function gradually decreases with age. After blood donation, as the number of blood cells decreases, the “dormant” bone marrow hematopoietic tissue is stimulated to remobilize and produce a large number of blood cells, so blood donation can keep the bone marrow vigorous and improve the hematopoietic function. Blood donation can also prevent cardiovascular diseases such as hypertension, because after donating blood, we will quickly fill up the blood volume by drinking water, and after blood dilution, blood lipids and other blood viscosity will be reduced. Adhering to long-term blood donation in the right amount, just like regularly dredging our circulatory system, can make our body relaxed, clear-headed and energetic. Blood donation is a reflection of social justice and fully reflects the idea of “we are for everyone and everyone is for me”. Why do some people feel fatigued and less resistant after donating blood for a short period of time? Some people also have heartburn and dizziness? This is because blood contains red blood cells, white blood cells and immune cells, and it takes some time for these cells to replenish after blood transfusion. Some people usually lack exercise or their bodies are overly sensitive. Once they lose some blood, their bodies appear to mobilize quickly, but it is more of a psychological effect – blood sickness, so some people will have some discomfort after blood donation, but after a quick adjustment, the discomfort will disappear quickly. It can be seen that if we are normally injured, the body surface abrasion, scratch bleeding or nosebleed, generally only a few milliliters or dozens of milliliters, there is no impact on health, but if the bleeding is more than that, it may have adverse effects on the human body, going to the hospital is the inevitable choice, but stop bleeding can not wait for the doctor to deal with, their own clean tissue pressure wound is the most simple and effective way to stop bleeding. As long as it is not a large blood vessel rupture, in fact, the bleeding will stop after a while of compression, go to the hospital for the purpose of dealing with the wound. As for the rest of the pressure bandages, tourniquets to stop bleeding and other methods are too professional, and the use of bad but damaging to the human body, here is not introduced. The bleeding of human internal organs and the bleeding after fracture is difficult to be estimated directly due to the amount and difficult to be stopped by compression, instead, it needs to be observed, examined and treated by doctors in time.